1. Field of the Invention
The present invention relates to a movable stage device for use with semiconductor printing apparatuses, machine tools or the like and a driving method for this device. In particular, it relates to a movable stage device requiring high speed and high accuracy in positioning and a driving method for the device.
2. Description of the Related Art
FIG. 13 is a top view of a conventional movable stage device of the above type; FIG. 14 is an enlarged sectional view taken along line E--E of FIG. 13.
This conventional movable stage device includes a stationary base 1 supported by two dampers 6.sub.1 and 6.sub.2 which constitute a stationary base supporting means having low rigidity and are adapted to dampen vibrations from a floor (see FIG. 14). Two guide plates 31.sub.1 and 31.sub.2 which constitute a guide means are provided at the right and left sides of the stationary base 1 (as seen in FIG. 14). A movable stage 2 is supported by the stationary base 1 and the guide plates 31.sub.1 and 31.sub.2 in a non-contact fashion through the intermediation of a plurality of fluid static pressure bearings (FIGS. 13 and 14 show only fluid static pressure bearings 32.sub.11, 32.sub.12, 32.sub.13, 32.sub.21, 32.sub.22 and 32.sub.23), and a linear motor 4 is provided on the stationary base 1 to constitute a driving means for imparting thrust to the movable stage 2 (see FIG. 14).
The linear motor 4 includes a yoke 42 fastened to the back surface of the movable stage 2 (the surface facing the stationary base 1) and having a rectangular hollow section. A group of drive coils 41 are arranged in a row along the stationary base 1 in the direction of movement of the movable stage 2 (i.e., horizontally) and are supported above the stationary base 1 by supports 35.sub.1 and 35.sub.2 at the respective ends of the row so that the row of coils extends through the hollow section of the yoke 42. A pair of permanent magnets 43.sub.1 and 43.sub.2 are mounted in the hollow section of the yoke 42. The movable stage 2 moves along the guide plates 31.sub.1 and 31.sub.2 when thrust is imparted to the stage by the linear motor 4. The distance the movable stage 2 moves is controlled according to positional information regarding the movable stage 2 obtained by a laser distance measurement system consisting of a mirror 52 fixed to the movable stage 2 and a laser distance measuring device 51.
The above-mentioned dampers 6.sub.1 and 6.sub.2 are provided between the stationary base 1 and the floor and have low rigidity because of their low resonance frequency so that vibrations from the floor are not transmitted to the stationary base 1. Thus, they serve to dampen any vibrations generated in the stationary base 1.
In this conventional movable stage device, the positioning of the movable stage 2 is effected quickly and with high accuracy by the following driving method. As shown in FIG. 15, for a long-distance movement, as in the case of moving the movable stage 2 from a stop position to a point near a target position, speed control is performed which allows movement at high speed. For accurate positioning of the stage 2 around the target position, position control is performed. To achieve high-speed movement during speed control, the linear motor 4 is used and, at the same time, an arrangement is adopted in which, as shown in FIG. 15, the speed of the stage is rapidly increased when it starts to move from the stop position and rapidly decreased directly before reaching the target position, thereby maintaining the maximum speed as high as possible and for as long a time as possible.
The conventional movable stage device, however, has the following problems:
(1) The reaction generated when imparting thrust to the movable stage 2 is received by the group of drive coils 41 of the linear motor 4 on the stationary base 1, and the rigidity of the dampers 6.sub.1 and 6.sub.2 is insufficient to dampen the reaction, so that increasing abrupt acceleration and deceleration of the movable stage at the time of speed control results in a proportionally increasing reaction, thereby causing the stationary base 1 to shake to a large degree. Therefore, at the time of position control, the movable stage 2 is shaken by the vibration of the stationary base 1. Thus, the conventional device does not help shorten the time taken for final positioning; on the contrary, the conventional device takes a relatively long time to effect final positioning.
(2) The vibration of the stationary base 1 causes its posture to change, thereby changing the posture of the movable stage 2. Thus, when applied to a machine tool or the like, the device will cause deterioration in machining precision. When applied to a semiconductor printing device, the device will cause deterioration in resolution since the focal point of the printing light will be shifted due to the tilting of the stage.
(3) Once the stationary base 1 has begun to shake, there is no means for effectively stopping its vibration; there is nothing to do but to wait for the vibration to subside by itself and cease to have any influence on the operation being performed.
(4) Effecting rapid acceleration and deceleration by using a large-thrust linear motor 4 results in an increase in the quantity of heat generated in the linear motor, thereby causing the movable stage 2, etc. to be deformed by heat. Therefore, when this device is applied to a machine tool or the like, the deformation by heat of the movable stage 2 causes the distance between the mirror 52 and the machining point to change, resulting in deterioration in machining precision. In the case when it is applied to a semiconductor printing apparatus, this device will cause deterioration in printing accuracy because of the changes caused in the distance between the mirror 52 and the printing position.
(5) The consumption of the thrust of the linear motor 4 in shaking the stationary base 1 leads to a waste of energy. These problems and others are addressed and overcome by the present invention.